Electric apparatus

ABSTRACT

A lightning arrester is disclosed including a volume of electrically negative fluid and a pair of spaced arcextinguishing plates formed of a copolymer of acetal including C-C- bonds.

Unlted States Patent 1151 3,662,221 Yamada et al. [4 1 May 9, 1972 [541 ELECTRIC APPARATUS [56] References Cited [72] Inventors: Naoya Yamada, Yao; Shoji Tada, UNITED STATES PATENTS 2,620,453 12/1952 Beese etal.... ..317/62x 1 Assign: Milsubishi Denki Kabushiki Kaisha, 3,450,923 6/1969 Brumm ..317/62 x Tokyo, Japan 22 Fil d; June 14, 1971 Primary Examiner-James D. Trammell [21]. AP 1 No 152 8 2 Attorney-Robert E. Burns 57 ABSTRACT 233%: A lightning arrest is disclosed indudinga volume ofelecm [58] Fieid 0'1'e;;;1;'IIIII.......1II3'i/& i"e5 '5'157167, 161,203 negaive fluid a Pair Spaced plates formed of a copolymer of acetal including CC bonds.

3 Claims, 3 Drawing Figures CHARACTERISTIC ELEMENT SURFACE RESISTANCE PATENTEDMAY 91912 3,662,221

24 CHARACTERISTIC 2 ELEMENT m l 2 7 (I f, 0.2- m g 4/2/- F NUMBER OF INTERRUPTIONS OF /6. 3 FOLLOW CURRENT IN MEGOHMS NUMBER OF INTERRUPTIONS OF FOLLOW CURRENT ELECTRIC APPARATUS BACKGROUND OF THE INVENTION cally negative fluids, high in arc-extinguishing and electrically insulating properties, such as gaseous SF Sci- C,F,,, C F C F,, SiF NF etc.. However if such an electrically negative fluid is exposed to the electric arc then those electrically insulating materials directly contacted by or disposed adjacent the electric arc exhibit a remarkable decrease in insulation resistance. Accordingly, homopolymers of acetal are presently employed as insulating materials particularly excellent in are proof and tracking resisting properties and creeping insulation characteristic within the electrically negative fluids. If the arcing portion is attempted to be diminished an energy per unit area of the surface to be treated becomes high. Therefore if an insulation formedof a homopolymer of acetal is disposed adjacent the arcing portion, the diminition of the arcing portion is not only restricted by its thermal endurance but also the surface of the insulation may damage after a great number of arcing operations will have been performed.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention to eliminate the abovementioned disadvantages of arc resisting materials used with electric apparatus employing electrically negative fluids of the conventional type as the arc-extinguishing material or the electrically insulating medium.

The invention accomplishes the objectby the provision of an electric apparatus comprising an arcing portion, a volume of electrically negative fluid serving as an arc-extinguishing material or as an electrically insulating medium disposed adjacent the arcing portion, and an arc resisting insulation contacted by the electrically negative fluid, characterized in that the arc resisting insulation is fonned of a copolymer of acetal containing -CC- bonds.

Preferably the electrically negative fluid may be a gas selected from the group consisting of gaseous SF SeF C,F,, C F C 5,, SiF,and NF A preferred electric apparatus embodying the principles of the invention may comprise a pair of spaced arc-extinguishing plates, a pair ofdischarge electrodes disposed between the arc-extinguishing plates, one driving coil disposed adjacent that side of each of the arc-extinguishing plates remote from the discharge electrodes to drive an electric arc, and a characteristic element, the main discharge electrodes, the driving coils and the characteristic element being electrically connected in series circuit relationships while being disposed within an electrically negative fluid, the pair of arc-extinguishing plates being formed of a copolymer of acetal containing CC- bonds.

BRIEF DESCRIPTION OF THE DRAWING The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a fragmental longitudinal sectional view of an electric apparatus embodying the principles of the invention;

FIG. 2 is a graph illustrating a weight loss of an arc-extinguishing plate constructed in accordance with the principles of the invention; and

FIG. 3 is a graph illustrating an electrical insulation characteristic of an arc-extinguishing plate described for FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing and FIG. 1 in particular, there is illustrated a lightning arrester embodying the principles of the invention. It is to be understood however that the invention is'not restricted to lightning arresters and that it is equally applicable to a variety of electric apparatus having the electric are developed therein. The arrangement illustrated comprises a pair of arc-extinguishing plates 10 and 12disposed in spaced parallel relationship and a pair of main discharge electrodes 14 and 16 disposed longitudinally aligned relationship between the arc-extinguishing plates 10 and 12 are provided on the inner opposite surfaces with indentations (not shown) suitable for interrupting the power-frequency follow current and the main discharge electrodes 14 and 16 form between the adjacent ends an arc gap 18 across which an electric arc is permitted to be developed.

The arrangement further comprises a pair of driving coils 2 and 22 disposed adjacent those sides of the arc-extinguishing plates 10 and 12 remote from the main discharge electrodes 14 and 16 to drive an electric are developed across the gap 18 and having the number of turns sufficient to extinguish the arc. The driving coils 20 and 22 are electrically connected to the discharge electrode 16 and 14 respectively with the coil 22 connected to ground through a characteristic element 24.

All the structural components as above described are disposed in place within a weatherproof enclosure (not shown) filled with a volume of any suitable electrically negative fluid 26 selected from the group consisting of gaseous SF SeF C,F,,, C F SiF NF etc..

In the arrangement illustrated, all the insulations including the arc-extinguishing plates 10 and 12 are required to be good in creeping insulation characteristic for long time. According to the principles of the invention, such insulations should be formed of a copolymer of acetal high in melting point and including highly crystal line chain molecules or a substrate made of any of epoxy, phenol and melamine resins and covered by a layer of such a copolymer of acetal. Alternatively the insulations can be formed of the substrate as above described having applied to one surface thereof a layer of the abovementioned copolymer of acetal intended to be contracted by the electrically negative fluid with satisfactory results.

The copolymers of acetal used with the invention are copolymers derived from troixane that is a trimer of fonnaldehyde and including the repeating units in the main chain molecules of polyoxymethylen and CC bonds therebetween and can be expressed by the structural formula (CI I,0)n (CC)n, (CH -0)n, (C-C)n, One examples of those polymers of acetals is sold by Polyplastic Co. under the trade mark Durakon" in Japan. Even if the copolymers of acetal have been initiated to be decomposedby the action of heat or for any other reason, the decomposition terminates at that C--C- bond first appearing in the straight chain -O--CI-I, of polyoxymethylene because the CC bonds high in bonding power are inclined in the straight chain thereof. This termination of the decomposition ensures that the depolymerization is prevented from further proceeding. Therefore the copolymers of acetals used with the invention have the excellent characteristics chemically and thermally stable as compared with the homopolymers of acetals previously employed for the same purpose. It has been found that such copolymers are successfully used as a material for the arc-extinguishing plates thereby to improve the thermal endurance thereof.

FIGS. 2 and 3 show the results of experiments conducted with models of the arc-extinguishing plate for the lightning arrester in which the interruptions of the power frequency follow current were effected many times. In FIG. 2, the axis of abscissas represents the number of the interruptions of the follow current and the axis of ordinates represents a thermal weight loss of the plate due to the occurrent interruptions. Straight line .A" depicts a thermal weight loss with the arcextinguishing plate formed of a homopolymer of acetal previously employed and straight line 8" describes the similar loss with the arc-extinguishing plate embodying the principles of the invention. From FIG. 2 it is seen that the use of the copolymer of acetal including the -C-C bonds decreases the thermal weight loss to about one-twelfth that caused from the use of homopolymers of acetals previously employed. This results in a great increase in useful life of the arc-extinguishing plate.

FIG. 2 is a graph plotting a surface resistance in megohms along the axis of ordinates against the number of the interruptions of the follow current along the axis of abscissas. In FIG. 3, curves A", B, C" and D were obtained with a phenol resin, a molding of mica mixed with glass having the medium quality, a polycarbonate resin and a molding of mica mixed with glass having the superior quality respectively. Curve E was obtained with a copolymer of acetal including --CC bonds according to the principles of the invention. In FIG. 3 it is noted that the copolymer of acetal has the surface resistance remaining substantially unchanged even after the follow current has been interrupted many times.

From the foregoing it will be appreciated that a lightning arrester filled with SF., gas has been provided which is high in performance, excellent in insulation characteristic and long in useful life through the formation of the arc-extinguishing, electrically insulating gap members of a copolymer of acetal including the -CC bonds.

It has been found that in electric apparatus other than lightning arresters having the electric are developed therein the copolymers of acetal as above described are used to form 'insulations contacted by the electrically negative fluid such as gaseous SP SeF C F C F C F SiF NF or the like serving as an arc-extinguishing medium or an electrically insulating medium disposed adjacent the arcing portion thereby to much improve the thermal endurance of the insulations resulting in a long useful life and also in a good insulation characteristics.

Therefore the invention has provided electric apparatus including the arc proof, electrically insulating portion contacted by the electrically negative fluid, the electric are or a high temperature gas resulting from the arc and much improved in thermal endurance, and increased in useful life as well as exhibiting the excellent insulation characteristics.

What we claim is:

1. In an electric apparatus, the combination of an arcing portion, a volume of electrically negative fluid serving as a selected one of an arc-extinguishing material and an electrically insulating medium disposed adjacent the arcing portion, and an arc resisting insulation contacted by the electrically negative fluid, and formed of a copolymer of acetal containing CCbonds.

2. An electric apparatus as claimed in claim 1, wherein the electrically negative fluid is a gas selected from the group consisting of gaseous SF SeF C F C F C,F,, SiF and NF 3. In an electric apparatus the combination of a pair of spaced arc-extinguishing plates, a pair of main discharge electrodes disposed between the arc-extinguishing plates, one driving coil disposed adjacent that side of each of the arcextinguishing plate remote from the main discharge electrodes to drive an electric arc and a characteristic element, the discharge electrodes, the driving coils and the characteristics element being electrically connected in series circuit relationship while being disposed within an electrically negative fluid, the pair of arc-extinguishing plates being formed of a copolymer of acetal containing C-C- bonds.

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2. An electric apparatus as claimed in claim 1, wherein the electrically negative fluid is a gas selected from the group consisting of gaseous SF6, SeF6, C2F6, C8F8, C4F8, SiF4and NF3.
 3. In an electric apparatus the combination of a pair of spaced arc-extinguishing plates, a pair of main discharge electrodes disposed between the arc-extinguishing plates, one driving coil disposed adjacent that side of each of the arc-extinguishing plate remote from the main discharge electrodes to drive an electric arc, and a characteristic element, the discharge electrodes, the driving coils and the characteristics element being electrically connected in series circuit relationship while being disposed within an electrically negative fluid, the pair of arc-extinguishing plates being formed of a copolymer of acetal containing ''''-C-C-'''' bonds. 